fix(aws-lambda) Fix typo in X-Amz-Function-Error header

[erran]

HTTP/1.1 200 OK
Content-Type: application/json
Connection: keep-alive
Content-Length: 444
Connection: keep-alive
x-amzn-RequestId: ...
X-Amzn-Trace-Id: ...
Date: Thu, 06 Jul 2017 16:23:07 GMT
X-Amz-Function-Error: Handled
x-amzn-Remapped-Content-Length: 0
Server: kong/0.10.2

Today I noticed that I mistakenly added a n to the aws lambda function http header. ☹️

This fixes the aws-lambda plugin and specs to use the correct function header name as per the latest documentation at http://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html#API_Invoke_ResponseSyntax

Response Syntax

HTTP/1.1 StatusCode
X-Amz-Function-Error: FunctionError
X-Amz-Log-Result: LogResult

Payload

I'll open a separate PR to support updating the status code for Handled errors.

suggested reviewers: @thibaultcha and @p0pr0ck5 since they helped me land #2587.

[thibaultcha]

Nice catch! Sorry that we let this slip through!

[thibaultcha]

Would it make sense to use the same prefix as well here? X-Amz-RequestId?

[erran]

@thibaultcha this is actually correct based on the response from Lambda (you can see the response headers in my original issue comment).

[thibaultcha]

Interesting... They have different response headers prefixes then... 🤔 LGTM then!

[erran]

Nice catch! Sorry that we let this slip through!

@thibaultcha yea, was confused when I created a custom plugin for testing since we'll start depending on these changes out today (we were previously pushing back until 10.4 was released).

After these changes the response code is correctly updated for unhandled errors (I'll add handled error support in another PR).

Next time around we'll have the automation ready to test custom plugins on our kong installations vs. depending on unit tests etc. 👌